1. Field of the Invention
This invention relates to exhaust gas recirculation (EGR) systems, and more particularly to EGR systems that draw a portion of exhaust gases through valves back into combustion chambers of four-stroke, internal combustion, compression-ignition engines.
2. Background Art
Exhaust gas recirculation (EGR) is a known approach to reducing diesel engine emissions. In typical internal combustion engines, fuel is mixed with air and ignited in a combustion chamber. Air comprises roughly 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases. Fuel and oxygen take part in combustion and, at sufficiently high temperatures, normally inert nitrogen reacts with the oxygen to form nitric oxide (NO). Upon being released into the atmosphere, nitric oxide readily oxidizes to form toxic nitrogen dioxide (NO2). This can be photochemically decomposed by sunlight to form nitric oxide and atomic oxygen, and the latter can initiate a reaction to form ozone.
Temperature has the greatest influence on the rate of formation of nitric oxide from atmospheric nitrogen. The reduction of combustion temperatures in an engine generally reduces the production of oxides of nitrogen (NOx), and combustion temperatures can be reduced by the presence in combustion chambers of a portion of exhaust gases produced during a previous cycle of the engine.
There are three common methods for ensuring the presence of exhaust gases. The first includes an external EGR system that routes a portion of exhaust gases from an engine's exhaust manifold to an engine's intake manifold. In this method, the exhaust gases are mixed with intake air before being drawn into the engine's combustion chambers through its intake valves. The second method retains a portion of the exhaust gases from a previous cycle within the engine's combustion chambers. The third method includes an internal EGR system that draws a portion of the exhaust gases from a previous cycle back into the engine's combustion chambers through its exhaust valves. The present invention represents a novel device for drawing exhaust gases into combustion chambers through valves controlled by intake rocker arms.